The present invention relates to a improved stackable columns used in the construction of multi-floor steel-framed buildings and to methods of constructing such buildings using a stackable column. More particularly, the present invention relates to apparatus and methods of stacking and coupling together hollow vertical columns for supporting successive floors of a multi-floor steel-framed building. As disclosed infra, an integral part of the present invention is a novel coupler.
Multi-floor steel-framed buildings are typically constructed with columns spanning the full height of the building, with intermediate floors framed with structural beams or joints on which a floor is laid. For ease in erection, it is highly desirable to construct each multi-floor column by a series of single floor columns, with each column aligned with, and structurally connected to, the column on the floor above and below. The alignment is important for load bearing reasons and locating the column in the floor below is often problematic once the floor is in place. Each joint in the column represents a potential weak link and some overlapping and bracing connection of adjacent column members in the column is important. In many instances, the columns provide all of the lateral stability of the building in resisting high winds and seismic events.
The column on each floor must bear the weight of the floor/ceiling immediately above it (the “floor load”). The floor typically includes horizontal beams and the floor structure laid on such beams, e.g. composite metal deck overlaid with concrete. The support of such floor is generally transferred to the column by the attachment of the beams thereto in shear through beam connectors. The floor load may be, but often is not, the same for successive floors.
In addition to the floor load, each lower column must support (a) the upper column immediately above it together with any floor/ceiling structure such upper column supports and (b) any additional column(s) above the upper column together with any floor/ceiling structure supported by such additional columns (collectively, the “column load”). The column load typically diminishes as the building rises because the column on higher floors has fewer columns above it to support. Because the column load may be significantly different from the floor load, the methods of transferring the column load and the floor load to the columns may also be different.
The stackable column art is highly developed. It is common in the construction of multi-floor buildings such as government housing, college dormitories, and storage facilities, that the column load on each floor be supported in compression by the lower column, e.g. by direct abutment of the column walls of the upper and lower columns. In addition to vertical alignment, it is desirable that the shape and cross-section area of upper and lower columns be identical to maximize the transfer in compression of the load of the upper column to the walls of the lower column. However, this uniformity of column size and shape is often undesirable as the column load of successive floors typically diminishes as the building rises. Thus, there may be a desire to use smaller diameter and/or reduced cross-section columns on successive floors, i.e., each being adequate for the floor load and reduced column load it must bear. It one aspect, the present invention provides a stackable column that effects transfer of column load from an upper column to a lower column in compression without the necessity for exact column registration or abutment.
Because of the desire to use identical factory fabricated columns, the prior art has adopted the use of relatively short length couplers to telescopingly receive the ends of adjacent columns in a stack. Such couplers often are provided with laterally extending beam connectors to which the floor supporting beams are bolted on site.
The floor load is transferred through these connectors to the lower column by the attachment of the coupler to the lower column. The attachment of the beam connectors to the coupler is in shear, and known systems transfer the floor load from the coupler to the lower column in shear, by through-column fasteners or by welding the lower extremity of the coupler to the lower column. In another aspect, the present invention transfers the floor load from the coupler to the lower column in compression rather than shear.
If the coupler is attached in shear to the column by through-column bolts, the through-column apertures weaken the column and thus require increased column thickness and/or diameter. In addition, there are generally alignment problems with the prior art pre-punched apertures which may interfere with the abutting contact needed between the ends of the columns for the transfer of column load in compression. In addition, there is the risk that aperture misalignment may cause one of the two or more fasteners to take all of the shear load rather than sharing it, leading to successive fastener failure.
If the coupler is attached in shear to the column by welding, such welds typically are overhead welds which are very difficult to make on site. In addition, welding is possible only if the two metals are sufficiently close together, and the combination of variations manufacturing tolerances as to the size and shape on the columns and coupler may make welding the coupler to the column impossible without the use of filler bars.
It is an advantage of the present invention that both column load and floor load are transferred from the coupler to the lower column in compression and without welding to the column or the use of through-column apertures.
Floor loads are often unbalanced, e.g. the floor load is not the same on all four sides of columns at the corners of buildings or adjacent mezzanines. This result is an eccentricity or bending moment of the coupler about the column. The bean connectors of known prior art couplers are attached to the coupler both above and below the top of the lower column, and the bending moment is increased to the extent that it is applied at any point above the top of the lower column, In some embodiments, the present invention attaches the bean connectors to the coupler below the top of the lower column (See FIGS. 4 & 6) and thus materially reduces the bending moment that results from floor load. This reduction in the bending moment caused by the floor load is also beneficial in the transfer of column load (that includes such floor load) to the column beneath.
In some embodiments of the present invention, the length of the flat plate is extended so that the ends protrude beyond the external walls of the coupler. (See FIG. 7). This extension may be used to provide additional support for the metal deck laid on top of the beams. The extension may also be apertured and used for coupler-to-coupler tension cables. Thus, the present invention enhances building rigidity by coupler-to-coupler tension connections.
In other embodiments of the present invention, the width of the flat plate extending through the slots in opposing walls of the coupler is narrowed to created openings or slots between the lateral sides of the flat plate and the internal walls of the coupler. (See FIG. 8). Elongated column connector plates may be vertically inserted through such slots alongside the internal walls of the coupler. The ends of the connector plates that protrude above and below the coupler may be secured to the walls of the columns by welding or by piercing fasteners so as to avoid through-column apertures. The attachment of vertically adjacent of the stacked columns by these connector plates enhances the rigidity of the column and provides a tension and continuity connection. In still another aspect, the vertically adjacent columns of the present invention are connected in tension without through-column apertures.
It is known to support a composite steel-concrete floor by the beam connectors, i.e. to attach I-beams to the connectors of adjacent columns, to support corrugated metal decking on the upper flange of the I-beams, and to pour concrete over the decking. (See FIG. 6). The total thickness of the floor includes the height of the I-beam and the overlying composite floor. In construction where it is desirable to have less total floor thickness, it is known to support the decking on the upper surface of the lower flange of the I-beam, thus reducing the total thickness of the floor by the depth of the I-beams (See FIG. 10).
The reduced thickness of the floor requires a reduced height coupler (See FIG. 10), advantageous in that it permits the finishing of the concrete floor without the necessity of avoiding the upwardly extending couplers. However, this requires that the beam connectors extend both above and below the top of the lower column and this increases the risk of bending moments as discussed supra. This is offset by the extension of the flat plate beyond the coupler walls into the concrete which will resist any movement of the coupler.
The resistance to shear provided by the length of the weld of the beam connectors is also reduced, but the top of the beam connector may be horizontally extended to increase the weld length without increasing the height of the coupler. (See FIG. 11). Where unusual upward as well as the normal downward forces must be considered as required in many military applications, the lower end of the beam connector may also be horizontally extended and welded to the coupler, enhancing the strength of the coupler. (See FIG. 12).
There is an additional advantage of the present invention where the concrete of the composite floor rises to or slightly above the upper flange of the I-beams. The web of the beams may be apertured at spaced intervals and construction rebar inserted through the apertures. (See FIG. 13). When the concrete is poured, concrete also extends from one bay to the adjacent bay through these apertures around the rebar and thus provides a continuous span which increases the floor load capacity, increases the fire rating, reduces cracking and strengthens the beam/concrete composite action.
Additional rigidity and resistance to shear may be provided in the present invention by shear panels bounded by laterally adjacent columns, the floor and the bottom of the beam connecting the laterally adjacent columns. (See FIG. 14). Conventional C-shaped light gage metal tracks may be attached by piercing fasteners and C-shaped metal studs conventionally spaced along the tracks. A solid panel or decking may be attached to the studs to provide a skin or diaphragm. The use of shear panels in light gage construction is well known, but is of particular significance in the system of the present invention where the shear panels are anchored in structural steel columns and where the vertical connector plates efficiently transfer the chord forces of the shear wall in tension as well as compression.
Alternatively to shear panels, conventional X-bracing or tube bracing may be utilized. Where such bracing is desired, the coupler of the present invention may be modified (See FIG. 15) to vertically extend the attached beam connectors downwardly beyond the level of the beams to be attached, and upwardly above the level of the floor to be poured, to provide a place for the attachment of the structural steel angles (tension only) or tubes (compression and tension) used as braces.
The above and many other advantages will be readily apparent to one skilled in the art to which the invention pertains from a perusal of the claims, the appended drawings, and the following detailed description of the preferred embodiments.